body {
    background: url("../img/book-mall-bg.jpg") no-repeat;
}
.login-box {
    width: 30%;
    padding: 50px 30px 0;
    margin: 20% auto;
    border: 1px solid lightgray;
    border-radius: 15px;
    background-color: rgba(255,255,255,0.9);
}
